There is a considerable demand for devices designed to sample air in factories, power plants, mines, etc., to determine the quantity of dust in the air at any one time. The quantity of fine dust particles (5 microns and below) is of particular interest since these particles are carried into the lungs during respiration. The air sampling devices consist of a pump, generally powered by a battery, a separator for removing the larger particles and a filter unit for collecting the dust particles less than 5 microns in size. The filter unit -- a capsule, -- is weighed before exposure to contamination for a definite period of time and is weighed again at the end of the air sampling period.
One of the shortcomings of the prior art devices is the failure to provide means of assuring that all of the particulate matter collected during sampling is present when the filter unit is weighed to determine the quantity of dust per cubic meter of air. Another shortcoming of the prior art devices is the failure to provide means for preventing the accidental or intentional loss (tampering) of the amount of matter collected. Still another shortcoming is the absence in the market of an ultra-light weight filter unit whereby higher weighing accuracies may be obtained.
Federal regulations require that the filter be made of a non-hygroscopic material and that the weight of the removable filter unit not exceed 5 grams, and that it be pre-weighed by the manufacturer with an accuracy of plus or minus 0.1 milligrams.
One of the objects of the invention is to provide a filter unit that complies with the above-mentioned Federal Specifications.
It is another object of the invention to provide a portable filter unit that is designed to preserve the physical integrity and purity of the filter capsule prior to its exposure to contamination monitoring.
It is another object of the invention to provide a portable filter unit that is designed to prevent any loss of the matter collected by the filter capsule during or after exposure to contamination monitoring.
It is another object of the invention to provide a portable filter unit that is designed to preserve the physical integrity of the filter capsule after its exposure to contamination.
It is another object of the invenion to provide a portable filter unit designed to prevent tampering with the collection process prior, during or after exposure of the filter capsule to contamination monitoring.
It is another object of the invention to provide a portable filter unit designed to provide positive evidence that tampering with the unit was attempted.
It is another object of this invention to provide a filter capsule unit having a total weight of less than five grams so that the amount of matter collected can be accurately determined.
It is another object of the invention to provide an ultralight weight all-filter capsule so that increased accuracy in weighing may be achieved.